Scanning type induction heating

ABSTRACT

There is disclosed herein means for providing progressive or scanning type induction heating of an elongated workpiece by means of a multiturn induction coil wherein there is continuous relative axial movement between the load and the coil. Means are provided for tapping a part or parts of the induction coil toward the exit end thereof whereby a separate voltage adjustment may be made at the tapped section or sections wherefor the temperature of the moving load is highest toward the exit end of the inductor.

United States Patent [56] References Cited UNITED STATES PATENTS3,610,861 10/1971 Storey et a] .219! 10.69 2,911,510 11/1959 McNulty..2l9/10.71 X 2,452,197 10/ 1948 Kennedy ..219/l0.43 X

Howell Sept. 5, 1972 54 SCANNING TYPE INDUCTION 3,497,658 2/1970 Ross..219 10.79 x

HEATING 2,748,240 5/1956 McArthur ..219/10.75

3,153,132 10/1964 Greene ..219/10.75 [72] Charles wand Ohm 2,720,57710/1955 Lackner ..219/1075 [73] Assignee: Ajax MagnetherrnicCorporation,

- Warren, Ohio Primary Examiner-J. V. Truhe Assistant Examiner-B. A.Reynolds 22 FIled. March 10,1971 Ammey J H Slough [21] Appl.No.: 122,795

57 ABSTRACT 52 U.S. c1. ..219/10.71, 219/1075, 219 1079 There sdisclosed herein means for Providing P 51 Int. Cl. ..H05b 5/06 Siva orScanning yp induction heating of an elon- [58] Field of Search..219/10.43, 10.61,10.69,10.71, gated workpiece y means of a multituminduction coil wherein there is continuous relative axial movementbetween the load and the coil. Means are provided for tapping apart orparts of the induction coil toward the exit end thereof whereby aseparate voltage adjustment may be made at the tapped section orsections wherefor the temperature of the moving load is highest towardthe exit end of the inductor.

17 Claims, 8 Drawing Figures PATENTED E 51912 3.689726 SHEET 2 BF 3TEMPE/3'6 TURE UPLOAD SURF/4 CE F- 1. [NC 7'/-/ 0/ //v0 00 TOR co/b-l FFE //v VN TOR Char/es M, We

d H SAOUGH ATTORNEY SCANNING TYPE INDUCTION HEATING This inventionrelates to induction heating and particularly to progressive or scanningtype induction heating of an elongated workpiece within an inductioncoil wherein there is continuous relative axial movement between saidcoil and the workpiece.

In the scan type induction hardening of an elongated steel load, such asa steel cylinder, it is well known to utilize a solenoid type inductor;and where a deeper hardened case depth is required, a multiturn solenoidtype induction coil is usually used.

Due to the characteristics of the magnetic field within the inductioncoil, a load continually passing therethrough reaches its highesttemperature axially inwardly from the exit end of the coil. In order tohave the load at the proper quenching temperature as it leaves theinduction coil, it is necessary to overheat the load within the coil.Excessive temperatures produce in the steel microstructure a conditioncalled grain growt Too much grain growth decreases the resistance of thesteel to quench cracking, fatigue cracking, and spalling in service.

The present invention is directed to providing an induction coil whereinthe power distribution along the coil is rearranged to overcome thisgrain growth or coarsening. This is accomplished by tapping a part orparts of the coil toward the exit end so that separate voltageadjustment at these tapped sections may be made to provide differentzones of heating. Increasing the voltage at the tapped sections raisesthe power level thereof relative to the power level at the untappedsection and will thus cause the cylinders hottest spot to be locatedtoward the exit end of the inductor.

It is an object of this invention to provide scan type induction heatingmeans wherein an elongated, con tinuously moving load reaches itshighest temperature substantially as it emerges from the induction coil.

Another object of the invention is to provide a scan type, multiturnsolenoid induction coil having means for redistributing the voltagewhereby to raise the power level thereof proximate to the exit end ofsaid coil.

Still another object of this invention is to provide scan type inductionheating means for a continuously moving, elongated load which willprevent hardened microstructure grain size growth in the load andimprove the loads resistance to quench cracking, fatigue cracking, andspalling in service.

Other objects of the invention and the advantages thereof will beapparent from the following description and the accompanying drawings,in which said drawings:

FIG. 1 is a simplified, sectional view of a multiturn induction coil andload passing therethrough showing one form of electrical connection foraccomplishing the objects of this invention;

FIG. 2a is a diagram showing, by way of comparison, the distribution ofmagnetic field strength axially along an energized induction coil whilescan heating a carbon steel cylinder, both with and without applying theteaching of the present invention;

FIG. 2b is a diagram showing the distribution of magnetic field strengthaxially along an energized, empty, conventional, multiturn solenoidinductor;

FIG. 3 is a diagram showing the distribution of load surface temperatureover the axial length of the energized induction coil while scan heatinga carbon steel cylinder, both with and with out application of thepresent invention; and

FIG. 4-7 are simple electrical diagrams showing different ways ofconnecting an induction coil to a power source according to the presentinvention.

Referring now to the drawings in all of which like parts are designatedby like reference numerals, in FIG. 1 there is shown a multiturnsolenoid type induction coil 10 made up of a plurality of helical turns11 of a preferably hollow, liquid cooled inductor. The induction coil 10is typically provided with a refractory lining 12 which defines acentral opening 13 therein through which an elongated load or workpiecesuch as a steel cylinder 14 is passed for continuous heating. Arrows Aand B indicate the directions of relative movement between the cylinder14 and the induction coil 10. It will be readily understood that for thepurposes of this invention either the induction coil 10 may be fixed andthe cylinder 14 moved longitudinally therethrough or said cylinder maybe held in a fixed position with said induction coil being movedrelative thereto.

A voltage source for energizing the induction coil 10 is provideddiagrammatically by leads L1 and L2 with the lead L2 being disposedadjacent to the right-hand or exit end of the inductor as shown. Anautotransformer 17 is connected across the leads L1 and L2 and providedwith a tap switch 18 whereby the induction coil 10 is electricallydivided into an untapped section 10a and a relatively smaller tappedsection 10a disposed adjacent to its exit end. It will be readilyunderstood that adjustment of the autotransformer to increase thevoltage in the untapped portion 10a will thereby shift the distributionof power generated in the work cylinder 14 toward the exit end of theinductor.

The diagrams of FIGS. 2a and 2b, and 3 graphically illustrate the effectof the present invention as applied to the scan type induction hardeningof, for example, a steel cylinder. When alternating current is passedthrough an inductor, a magnetic field is generated within the inductor.When a load such as a steel cylinder is place in the inductor, it is thestrength of the magnetic field which determines the power generatedwithin the load. The strength of the magnetic field is not uniform alongthe length of the inductor as indicated by the dotted line 20 in FIG.2b, said dotted line indicating the approximate relative field strengthalong the length of an energized induction coil which is empty or whichheats a non-ferrous material. Quench hardenable steels have propertieswhich make the more easily magnetized than air or nonferrous materialswhereby for a given level of inductor current a carbon steel cylinderwill have a much greater magnetic field strength than a nonferrouscylinder of the same dimensions. However, as the carbon steel is heated,this magnetic effect is reduced, and when the temperature passes acertain critical point called the Curie point (l300l400 F.) it loses itsmagnetic properties. In scan hardening of a carbon steel cylinder it isnecessary to heat the cylinder beyond the Curie point and as a resultthe relative field strength along the length of the inductor is furtherchanged giving an even more reduced field strength toward the exit endof the inductor. This last mentioned phenomenon is illustrated by thedot-dash broken line 21 in the diagram of FIG. 2a.

Since the power generated in the workpiece is proportional to the squareof the magnetic field strength, there could be a substantial reductionin the power generated in the workpiece as it approaches the exit end ofthe inductor.

Thus it will be seen that in untapped induction coils, as the cylinderor load being heated progresses through the coil toward the exit end,the heat losses due to radiation, convection, and conduction tend toincrease while the heat generated within the cylinder tends to decrease.Experience has shown that where deep hardening is being done, the powerdensity is such that the surface temperature of the cylinder actuallydecreases as it passes through the exit end portion of the inductioncoil. This means that the highest cylinder surface temperature isreached not at the coil exit but somewhere closer to the axial center ofthe inductor. Therefore, in order to attain the minimum quenchtemperature needed at the exit end of the inductor whereby to developfull hardness in the cylinder, said cylinder must be overheatedsomewhere inwardly toward the medial portion of the induction coilwhereby when it leaves the coil, the temperature thereof will not havedropped below minimal quenching temperature. It is such overheating andexcessive temperatures which produce in the steel microstructure acondition called grain growth" which will decrease the resistance of thesteel to quench cracking, fatigue cracking, and spalling in service.

The present invention corrects the above situation and reduces thetendency to grain coarsening by tapping a part or parts of the inductioncoil toward the exit end thereof whereby a separate voltage adjustmentcan be made at this point. By raising the voltage level in the tappedsection b and thereby relatively decreasing it in the untapped section10a, a magnetic field strength distribution along the length of theinductor somewhat as indicated by the full line 22 of FIG. 2a, isattained. From the practical standpoint of the surface temperatureachieved, this comparison is illustrated in FIG. 3 where the dotted line24 illustrates the pattern of heat distribution over the length of theinduction coil when the present invention is not applied whereas thefull line shown at 25 indicates such temperature pattern when thepresent invention is utilized. Thus it will be clearly seen that in useof the present invention, the temperature is highest at the exit end ofthe induction coil thereby eliminating the need for overheating the loadfurther back in said coil. This allows a reduction in the maximumtemperature to which the cylinder is heated for hardening.

FIGS. 4-7 illustrate alternative approaches to applying the presentinvention whereby a certain tapped section or sections near the exit endof the inductor are provided with different voltages. In each simpleelectrical diagram, the induction coil is generally indicated at 10 withvoltage being supplied by the leads L1 and L2.

In FIG. 4, the induction coil 10 is provided with two zones of controlby means of two autotransforrners 27 and 28 having tap switches 29, 30,respectively, adjacent to the exit end of the coil. In this way, thevoltage and, therefore, the heating potential of the coil can beincreased toward the exit end in steps.

FIG. 5 also shows a two-zone control including a sin gle autotransformer32 having two tap switches 33 and 34 adjacent to the exit end of theinduction coil.

FIG. 6 shows a single-zone control adjacent to the exit end of theinduction coil which comprises a fixed autotransformer 36 and a tapswitch 37 providing for adjustment at the induction coil.

The final example of FIG. 7 is, again, a two-zone control comprising tapswitches 39 and 40 adjustably connecting a secondary winding 45 of amain transformer T with the induction coil 10 adjacent to the exit endthereof. An additional tap switch 42 is provided in the lead L2 andadjustably connects lead L2 to the primary winding 46 on the oppositeside of said transformer. Leads L1 and L2 connect the ends of thesecondary winding 45 to the ends of the induction coil 10.

All of the above examples of electrical connections provide meanswhereby the hottest point of a relatively moving load in a solenoid typeinduction coil occurs proximate to the exit end of the coil whereby toreduce the maximum temperature to which the load is heated and at thesame time provide the necessary quenching temperature at said exit end.

It will be understood that many changes in the details of the inventionas herein described and illustrated may be made without, however,departing from the spirit thereof or the scope of the appended claims.

Iclaim:

1. In a scanning type induction heater, a multiturn solenoid typeinduction coil having an entrance end and an exit end and adapted tocontinuously progressively heat an elongated load projecting throughsaid coil whereby the highest load temperature is attained adjacent tosaid exit end, the load and coil traveling axially with respect to eachother during heating; means for energizing said coil to heat the load toquenching temperature, said energizing means including means to applyrelatively increased voltage to that portion of said coil adjacent tosaid exit end wherefore every portion of the moving load attains auniform maximum temperature proximate to said exit end.

2. In a scanning type induction heater as set forth in claim 1: meansmodifying the power distribution including means electrically dividingthe portion of said coil adjacent to said exit end into at least twoadjacent zones whereby to increase the voltage in steps toward the exitend of said induction coil.

3. In a scanning type induction heater as set forth in claim 1: saidmeans for energizing said coil comprising power leads connected to theends of said induction coil; an autotransformer connected in parallelwith said induction coil; and tap means adjustably connecting an exitend portion of said induction coil with said autotransformer whereby thevoltage in the tapped portion of said coil is increased relative to theuntapped portion thereof to attain maximum temperature in the loadproximate to said exit end.

4. In a scanning type induction heater as set forth in claim 3: said tapmeans being located at said autotransformer for adjustment with respectthereto.

5. In a scanning type induction heater as set forth in claim 3: said tapmeans being located at said induction coil for adjustment with respectthereto.

6. In a scanning type induction heater as set forth in claim 1: saidmeans for energizing said coil comprising power leads connected to theends of said induction coil; a pair of autotransforrners connected inparallel with said induction coil; and a pair of adjustable tap meansconnecting an exit end portion of said induction coil with respective ofsaid autotransforrners whereby said exit end portion is divided into twozones of control for increasing the voltage in said zones relative tothe untapped portion of said coil in steps toward said exit end wherebythe spot at which the load attains maximum temperature is proximate tosaid exit end of said coil.

7. In a scanning type induction heater asset forth in claim 1: saidmeans for energizing said coil comprising power leads connected to theends of said induction coil; an autotransformer connected in parallelwith said induction coil; a pair of tap means adjustably connecting anexit end portion of said coil at two axially spaced points along saidcoil and autotransformer whereby said exit end portion is divided intotwo zones of control for increasing the voltage of said exit end portionrelative to the untapped portion of said coil in steps toward said exitend whereby the spot at which the load attains maximum temperature isproximate to said exit end of said coil.

8. In a scanning type induction heater as set forth in claim 1: saidmeans for energizing said coil comprising a main transformer havingprimary and secondary windings; a pair of power leads connected adjacentto the ends of said primary winding, one of said leads being adjustablyconnected to said primary winding by tap means; means connecting theends of said secondary winding to said induction coil; and an additionalpair of tap means adjustably connecting an exit end portion of said coilat two axially spaced points along said coil and secondary windingwhereby said exit end portion is divided into two zones of control forincreasing the voltage relative to the untapped portion of said coil insteps toward said exit end whereby the spot at which the load attainsmaximum temperature is proximate to said exit end of said coil.

9. In a scanning type induction heater as set forth in claim 1: saidmeans for energizing said coil comprising a main transformer havingprimary and secondary windings; a pair of power leads connected adjacentto the ends of said primary winding, one of said leads being adjustablyconnected to said primary winding by tap means; means connecting theends of said secondary winding to said induction coil; and tap meansadjustably connecting an exit end portion of said induction coil withsaid secondary winding whereby the voltage in the tapped portion of saidcoil is increased relative to the untapped portion thereof and wherebythe spot at which the load attains maximum temperature is proximate tosaid exit end of said coil.

10. In a scanning type induction heater, a multitum solenoid typeinduction coil having an entrance end and an exit end and adapted tocontinuously progressively heat an elongated load projecting through andhaving relative axial movement with respect to said coil and bringingevery portion of said load to its highest temperature adjacent to saidexit end; means for energizing said coil including power leads connectedto the ends of said induction coil; transformer means connected acrosssaid power leads in parallel with said in- ?uction coil; tap meansconnected betw en saidtransonner means and induction coil where y saidinduction coil is divided axially into a tapped section adjacent to saidexit end and an untapped section extending form said entrance end tosaid tapped section; said tap means providing an increased voltage levelin said tapped section relative to said untapped section and shiftingthe distribution of power generated in the load toward the exit end ofsaid induction coil whereby the temperature of every portion of themoving load reaches its highest level adjacent to said exit end.

1 1. In a scanning type induction heater as set forth in claim 10: saidtransformer means comprising an autotransforrner connected in parallelwith said induction coil.

12. In a scanning type induction heater as set forth in claim 11: saidtap means being adjustably connected at said autotransforrner foradjusting the voltage level in said sections of said coil.

13. In a scanning type induction heater as set forth in claim 11: saidtap means being adjustably located at said induction coil for adjustingthe voltage level in said sections thereof.

14. In a scanning type induction heater as set forth in claim 10: saiduntapped section being of greater axial extent than said tapped section.

15. In a scanning type induction heater as set forth in claim 10: saidtransformer means comprising a pair of autotransforrners each connectedin parallel with said induction coil; said tap means comprising a pairof adjustable taps connecting an exit end portion of said coil withrespective of said autotransforrners whereby said tapped section isdivided into two zones of control for increasing the voltage in saidzones relative to said untapped section in steps toward said exit end.

16. In a scanning type induction heater as set forth in claim 10: saidtransformer means comprising an autotransforrner; said tap meanscomprising a pair of adjustable taps connecting an exit end portion ofsaid coil at two axially spaced points along said coil andautotransformer whereby said exit end portion is divided into two zonesof control for increasing the voltage in said zones relative to saiduntapped section in steps toward said exit end.

17. In a scanning type induction heater as set forth in claim 10: saidtransformer means comprising a main transformer having primary andsecondary windings; said power leads comprising incoming lead portionsconnected adjacent to the ends of said primary winding, one of saidincoming lead portions being adjustably connected to said primarywinding; said power leads including connector lead portions connectingthe ends of said secondary winding to the ends of said induction coil;said tap means being adjustable at said coil whereby voltage in thetapped portion of said coil is increased relative to the untappedportion thereof.

1. In a scanning type induction heater, a multiturn solenoid typeinduction coil having an entrance end and an exit end and adapted tocontinuously progressively heat an elongated load projecting throughsaid coil whereby the highest load temperature is attained adjacent tosaid exit end, the load and coil traveling axially with respect to eachother during heating; means for energizing said coil to heat the load toquenching temperature, said energizing means including means to applyrelatively increased voltage to that portion of said coil adjacent tosaid exit end wherefore every portion of the moving load attains auniform maximum temperature proximate to said exit end.
 2. In a scanningtype induction heater as set forth in claim 1: means modifying the powerdistribution including means electrically dividing the portion of saidcoil adjacent to said exit end into at least two adjacent zones wherebyto increase the voltage in steps toward the exit end of said inductioncoil.
 3. In a scanning type induction heater as set forth in claim 1:said means for energizing said coil comprising power leads connected tothe ends of said induction coil; an autotransformer connected inparallel with said induction coil; and tap means adjustably connectingan exit end portion of said induction coil with said autotransformerwhereby the voltage in the tapped portion of said coil is increasedrelative to the untapped portion thereof to attain maximum temperaturein the load proximate to said exit end.
 4. In a scanning type inductionheater as set forth in claim 3: said tap means being located at saidautotransformer for adjustment with respect thereto.
 5. In a scanningtype induction heater as set forth in claim 3: said tap means beinglocated at said induction coil for adjustment with respect thereto. 6.In a scanning type induction heater as set forth in claim 1: said meansfor energizing said coil comprising power leads connected to the ends ofsaid induction coil; a pair of autotransformers connected in parallelwith said induction coil; and a pair of adjustable tap means connectingan exit end portion of said induction coil with respective of saidautotransformers whereby said exit end portion is divided into two zonesof control for increasing the voltage in said zones relative to theuntapped portion of said coil in steps toward said exit end whereby thespot at which the load attains maximum temperature is proximate to saidexit end of said coil.
 7. In a scanning type induction heater as setforth in claim 1: said means for energizing said coil comprising powerleads connected to the ends of said induction coil; an autotransformerconnected in parallel with said induction coil; a pair of tap meansadjustably connecting an exit end portion of said coil at two axiallyspaced points along said coil and autotransformer whereby said exit endportion is divided into two zones of control for increasing the voltageof said exit end portion relative to the untapped portion of said coilin steps toward said exit end whereby the spot at which the load attainsmaximum temperature is proximate to said exit end of said coil.
 8. In ascanning type induCtion heater as set forth in claim 1: said means forenergizing said coil comprising a main transformer having primary andsecondary windings; a pair of power leads connected adjacent to the endsof said primary winding, one of said leads being adjustably connected tosaid primary winding by tap means; means connecting the ends of saidsecondary winding to said induction coil; and an additional pair of tapmeans adjustably connecting an exit end portion of said coil at twoaxially spaced points along said coil and secondary winding whereby saidexit end portion is divided into two zones of control for increasing thevoltage relative to the untapped portion of said coil in steps towardsaid exit end whereby the spot at which the load attains maximumtemperature is proximate to said exit end of said coil.
 9. In a scanningtype induction heater as set forth in claim 1: said means for energizingsaid coil comprising a main transformer having primary and secondarywindings; a pair of power leads connected adjacent to the ends of saidprimary winding, one of said leads being adjustably connected to saidprimary winding by tap means; means connecting the ends of saidsecondary winding to said induction coil; and tap means adjustablyconnecting an exit end portion of said induction coil with saidsecondary winding whereby the voltage in the tapped portion of said coilis increased relative to the untapped portion thereof and whereby thespot at which the load attains maximum temperature is proximate to saidexit end of said coil.
 10. In a scanning type induction heater, amultiturn solenoid type induction coil having an entrance end and anexit end and adapted to continuously progressively heat an elongatedload projecting through and having relative axial movement with respectto said coil and bringing every portion of said load to its highesttemperature adjacent to said exit end; means for energizing said coilincluding power leads connected to the ends of said induction coil;transformer means connected across said power leads in parallel withsaid induction coil; tap means connected between said transformer meansand induction coil whereby said induction coil is divided axially into atapped section adjacent to said exit end and an untapped sectionextending form said entrance end to said tapped section; said tap meansproviding an increased voltage level in said tapped section relative tosaid untapped section and shifting the distribution of power generatedin the load toward the exit end of said induction coil whereby thetemperature of every portion of the moving load reaches its highestlevel adjacent to said exit end.
 11. In a scanning type induction heateras set forth in claim 10: said transformer means comprising anautotransformer connected in parallel with said induction coil.
 12. In ascanning type induction heater as set forth in claim 11: said tap meansbeing adjustably connected at said autotransformer for adjusting thevoltage level in said sections of said coil.
 13. In a scanning typeinduction heater as set forth in claim 11: said tap means beingadjustably located at said induction coil for adjusting the voltagelevel in said sections thereof.
 14. In a scanning type induction heateras set forth in claim 10: said untapped section being of greater axialextent than said tapped section.
 15. In a scanning type induction heateras set forth in claim 10: said transformer means comprising a pair ofautotransformers each connected in parallel with said induction coil;said tap means comprising a pair of adjustable taps connecting an exitend portion of said coil with respective of said autotransformerswhereby said tapped section is divided into two zones of control forincreasing the voltage in said zones relative to said untapped sectionin steps toward said exit end.
 16. In a scanning type induction heateras set forth in claim 10: said transformer means comprising anautotransformer; said tap means comprising a pair of adjustable tapsconnectinG an exit end portion of said coil at two axially spaced pointsalong said coil and autotransformer whereby said exit end portion isdivided into two zones of control for increasing the voltage in saidzones relative to said untapped section in steps toward said exit end.17. In a scanning type induction heater as set forth in claim 10: saidtransformer means comprising a main transformer having primary andsecondary windings; said power leads comprising incoming lead portionsconnected adjacent to the ends of said primary winding, one of saidincoming lead portions being adjustably connected to said primarywinding; said power leads including connector lead portions connectingthe ends of said secondary winding to the ends of said induction coil;said tap means being adjustable at said coil whereby voltage in thetapped portion of said coil is increased relative to the untappedportion thereof.